When to measure a rad temperature?

[DIYWell]

Panel rad, nothing fancy, lockshield on one end, TRV on the other. Fancy k type thermocouples clamped to the feed and return to measure the temperature drop. Boiler is an old fashioned non-condensing combi.

So when is the correct time to take a measurement? Too soon and the system is coming up to temperature, too late and the TRV has kicked in and the rad is cooling off anyway.

 

[Swwils]

Take the TRV off.

 

[DIYWell]

Take the TRV off.

You mean remove the head?

And how long would you give it from cold start of the boiler to taking a measurement?

 

[Swwils]

Depends on the output of the heat source and size of the system.

With the TRV off it won't matter will it, rad will never shut off.

If your boiler is so old it doesn't condense then little point in this exercise.

 

[ScottishGasMan]

Should take it when the room is 20-21 degrees. That's what design spec is. So if someone says X radiator should have a 10 degree difference between flow and return, then that would be when the radiator is at operating temperature (so when the boiler is still firing) and when the room is at 20-21 degrees.

 

[DIYWell]

If your boiler is so old it doesn't condense then little point in this exercise.

Care to explain why a temperature difference can only be measured when the boiler is a condensing boiler?